Ejecting assembly for a surgical stapler

ABSTRACT

An end effector includes first and second jaws, a drive screw, a lead screw nut, and a drive beam. The drive screw is disposed within the first jaw. The lead screw nut defines a threaded bore that receives the drive screw. The lead screw nut is advanced along the drive screw as the drive screw is rotated in a first direction and is retracted along the drive screw as the drive screw rotates in a second direction. The drive beam is releasably coupled to the lead screw nut when the lead screw nut is in a retracted position. As the lead screw nut is advanced the drive beam is pulled by the lead screw nut. The drive beam is decoupled from the lead screw nut as the lead screw nut is advanced such that the lead screw nut is advanced relative to the drive beam.

BACKGROUND

1. Technical Field

The present disclosure relates to surgical apparatus, devices, and/orsystems for performing endoscopic surgical procedures and methods of usethereof. More specifically, the present disclosure relates toelectromechanical, hand-held surgical apparatus, devices, and/or systemsconfigured for use with removable disposable loading units and/or singleuse loading units for clamping, cutting, and/or stapling tissue.

2. Description of Related Art

A number of surgical device manufacturers have developed product lineswith proprietary drive systems for operating and/or manipulatingelectromechanical surgical devices. Some electromechanical surgicaldevices include a handle assembly, which is reusable, and replaceableloading units and/or single use loading units or the like that areselectively connected to the handle assembly prior to use and thendisconnected from the handle assembly following use, in order to bedisposed of or in some instances sterilized for re-use.

Many of these electromechanical surgical devices are relativelyexpensive to manufacture, purchase, and/or operate. There is a desire bymanufacturers and end users to develop electromechanical surgicaldevices that are relatively inexpensive to manufacture, purchase, and/oroperate.

Accordingly, a need exists for electromechanical surgical apparatus,devices and/or systems that are relatively economical to develop andmanufacture, to store and ship, as well as economical and convenient topurchase and use from the end user's perspective.

SUMMARY

In an aspect of the present disclosure, an end effector includes firstand second jaws moveable relative to one another, a drive screw, a leadscrew nut, and a drive beam. The drive screw is disposed within thefirst jaw and defines a longitudinal axis. The lead screw nut defines athreaded bore that receives the drive screw therethrough. The lead screwnut is advanced along the drive screw as the drive screw is rotated in afirst direction and is retracted along the drive screw as the drivescrew rotates in a second direction that is opposite to the firstdirection. The drive beam is releasably coupled to the lead screw nutwhen the lead screw nut is in a retracted position. The drive beam ispulled by the lead screw nut as the lead screw nut is advanced towards afirst advanced position. The drive beam decouples from the lead screwnut as the lead screw nut is advanced to the first advanced positionsuch that the lead screw nut is advanced relative to the drive beam fromthe first advanced position to a second advanced position. The drivebeam may define a passage that receives the drive screw therethrough.

In aspects, the end effector may include a sled that defines a channelthat receives the drive screw and is configured to guide the sled alongthe drive screw. The lead screw may be spaced apart from and positionedproximal to the sled in the retracted position. The lead screw nut mayengage a proximal surface of the sled at the first advanced position.The lead screw nut may push the sled distally as the lead screw nut isadvanced from the first advanced position towards the second advancedposition.

In some aspects, the first jaw may include a cartridge assembly thatincludes staples disposed therein. As the lead screw is advanced fromthe first advanced position towards the second advanced position, thesled may eject the staples from within the cartridge assembly towardsthe second jaw. The cartridge assembly may include a staple pusherassociated with each of the staples such that the sled sequentiallyengages the staple pushers to eject the staples from within thecartridge assembly. When the lead screw nut is retracted to the firstadvanced position after pushing the sled, the sled may remain stationaryin a position between the first and second advanced positions. When thelead screw nut is retracted from the first advanced position towards theretracted position, the lead screw nut pushes the drive beam towards theretracted position and couples to the drive beam.

In certain aspects, the end effector includes a latch having anelongated portion with proximal and distal ends. The proximal end of theelongated portion is pivotally coupled to the drive beam and the distalend of the elongated position includes a bridge. The bridge may bereceived within a notch defined by the lead screw nut when the leadscrew nut is in the retracted position to couple the drive beam to thelead screw nut. When the lead screw nut is advanced towards the firstadvanced position, the bridge may be raised out of the notch to decouplethe drive beam from the lead screw nut. When the lead screw nut isretracted from the first advanced position towards the refractedposition, the bridge may be lowered into the notch to couple the drivebeam to the lead screw nut.

In particular aspects, the end effector includes a cam member that ispositioned adjacent the drive screw and defines a cam slot. The cam slotmay have first portion that is parallel to the longitudinal axis of thedrive screw and a second portion that extends distally from the firstportion at an angle relative to and away from the longitudinal axis ofthe drive screw. The distal end of the elongated portion may include apin that is slidably received in the cam slot. The bridge may bereceived in the notch when the pin is in the first portion of the camslot and the bridge may be raised out of the notch as the pin slidesdistally along the second portion of the cam slot.

In another aspect of the present disclosure, a surgical instrumentincludes a handle, a shaft extending from the handle, and an endeffector supported at a distal end of the shaft. The end effector may beany of the end effectors disclosed herein.

In yet another aspect of the present disclosure, a method of ejectingstaples from a cartridge assembly includes providing an end effector,coupling a cartridge assembly to the first jaw, advancing a lead screwnut towards a first advanced position, and advancing the lead screw nutfrom the first advanced position. The end effector may be any of the endeffectors disclosed herein. Advancing the lead screw nut towards a firstadvanced position is accomplished by rotating a drive screw in a firstdirection. The drive beam being pulled by the lead screw nut as the leadscrew nut is advanced towards the first advanced position. The drivebeam decoupling from the lead screw nut as the lead screw nut reachesthe first advanced position. As the lead screw nut is advanced from thefirst position, the drive beam remains stationary and the lead screw nutpushes the sled through the cartridge assembly to sequentially eject thestaples.

In aspects, the method includes retracting the lead screw nut from thesecond advanced position towards the first advanced position by rotatingthe drive screw in a second direction opposite the first direction. Thesled remaining stationary as the lead screw nut is retracted. The methodmay include retracting the lead screw nut from the first advancedposition towards a refracted position. The drive beam coupling to thelead screw nut as the lead screw nut is retracted from the firstadvanced position.

In some aspects, the drive beam decouples from the lead screw nut byraising a bridge of a latch that is operatively associated with thedrive beam out of a notch defined by the lead screw nut.

In certain aspects, the drive beam couples to the lead screw nut bylowering a bridge of a latch operatively associated with the drive beaminto a notch defined by the lead screw nut.

Further, to the extent consistent, any of the aspects described hereinmay be used in conjunction with any or all of the other aspectsdescribed herein.

BRIEF DESCRIPTION OF THE DRAWING

Various aspects of the present disclosure are described hereinbelow withreference to the drawings, which are incorporated in and constitute apart of this specification, wherein:

FIG. 1 is a perspective view of a surgical instrument in accordance withthe presented disclosure with the parts separated;

FIG. 2 is a perspective view of the end effector of FIG. 1;

FIG. 3 is a side perspective view of the end effector of FIG. 2, withthe upper jaw and the housing of the lower jaw removed, in a retractedposition;

FIG. 4 is a top view of the end effector of FIG. 3;

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 4;

FIG. 6 is a side perspective view of the end effector of FIG. 2, withthe upper jaw and the housing of the lower jaw removed, in a firstadvanced position;

FIG. 7 is a top view of the end effector of FIG. 6;

FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 7;

FIG. 9 is a side perspective view of the end effector of FIG. 2, withthe upper jaw and the housing of the lower jaw removed, in a secondadvanced position;

FIG. 10 is a top view of the end effector of FIG. 9; and

FIG. 11 is a cross-sectional view taken along the line 11-11 of FIG. 10.

DETAILED DESCRIPTION

Embodiments of the present disclosure are now described in detail withreference to the drawings in which like reference numerals designateidentical or corresponding elements in each of the several views. Asused herein, the term “clinician” refers to a doctor, a nurse, or anyother care provider and may include support personnel. Throughout thisdescription, the term “proximal” refers to the portion of the device orcomponent thereof that is closest to the clinician and the term “distal”refers to the portion of the device or component thereof that isfarthest from the clinician. The terms “left” and “right” refer to thatportion of the electromechanical surgical system, apparatus and/ordevice, or component thereof, that are on the left and right (sides,respectively, from the perspective of the user facing the distal end ofthe electromechanical surgical system, apparatus and/or device from theproximal end while the surgical system, apparatus and/or device isoriented in non-rotational configuration.

Referring initially to FIG. 1, an end effector in accordance with anembodiment of the present disclosure is shown and generally designated10. The end effector 10 may be connected to various surgical staplinginstruments, e.g., manual or powered surgical stapling instruments. Forillustrative purposes, the end effector 10 is described herein asconfigured to connect to a surgical apparatus or device in the form ofan electromechanical, hand-held, powered surgical instrument 100. Thesurgical instrument 100 includes an adapter assembly (e.g., elongatedbody) 200 that connects to the end effector 10. The end effector 10 andthe adapter assembly 200 are configured for actuation and manipulationby the electromechanical, hand-held, powered surgical instrument 100. Inparticular, the surgical instrument 100, the adapter assembly 200, andthe end effector 10 are separable from each other such that the surgicalinstrument 100 is configured for selective connection with the adapterassembly 200, and, in turn, the adapter assembly 200 is configured forselective connection with any one of a plurality of different endeffectors.

Briefly, the hand-held surgical instrument 100 includes a handle housing102 having a lower housing portion 104, an intermediate housing portion106 extending from or supported on lower housing portion 104, and anupper housing portion 108 extending from or supported on intermediatehousing portion 106. Intermediate housing portion 106 and upper housingportion 108 are separated into a distal half-section 110 a that isintegrally formed with and extending from the lower portion 104, and aproximal half-section 110 b connectable to the distal half-section 110 aby a plurality of fasteners. When joined, the distal and proximalhalf-sections 110 a, 110 b define a handle housing 102 having a cavity(not shown) therein in which a circuit board (not shown) and a drivemechanism (not shown) are situated.

It is contemplated that the handle can be manually operated, powered bya motor, and/or include a computerized controller or controllers. Theend effector may be removable and replaceable and may house a staplecartridge that also may be removable and replaceable. The end effectorand/or cartridge can include computerized microchips or mechanicalfeatures that are used in the identification of those components. Memoryunits can be included, such as EEPROMs, similar memory devices, and/orDallas one wire chips. The adapter can be separately removable andreplaceable, or be integral with the handle, and can have its ownidentification and/or memory features.

With continued reference to FIG. 1, the adapter assembly 200 isconfigured to communicate rotational forces provided by the surgicalinstrument 100 to the end effector 10. The adapter assembly 200 includesan elongate, substantially rigid, elongate body portion 210 having aproximal end 210 a and a distal end 210 b. A transmission housing 212 isconnected to the proximal end 210 a of the elongate body portion 210 andis configured for selective connection to the surgical instrument 100.The adapter assembly 200 includes an articulating assembly 230 disposedat the distal end 210 b for coupling to the end effector 10. Thetransmission housing 212 of the adapter assembly 200 connects to aconnecting portion 108 a of an upper housing portion 108 of the surgicalinstrument 100 via a shaft coupling assembly 214, which is supported atthe proximal end 210 a.

Exemplary examples of electromechanical, hand-held, powered surgicalinstruments and adapters are disclosed in commonly owned and co-pendingU.S. patent application Ser. No. 13/331,047, filed Dec. 20, 2011 andpublished as U.S. Patent Pub. No. 2012/0089131 on Apr. 12, 2012, andSer. No. 13/484,975, filed May 31, 2012 and published as U.S. PatentPub. No. 2012/0253329 on Oct. 4, 2012, the contents of each are herebyincorporated by reference in their entirety.

Referring to FIGS. 1 and 2, the end effector 10 includes a first jaw 12that includes a carrier or housing 18 which is configured to releasablycouple to a cartridge assembly 16 (FIG. 2). The end effector 10 includesa second jaw 14 in the form of an anvil. The cartridge assembly 16houses one or more fasteners 310 (FIG. 3) that are disposed therewithinand is configured to deploy the fasteners 310 upon firing of instrument100. The second jaw 14 is mounted to the end effector 10 and is movablewith respect to the first jaw 12 between an open position, wherein thesecond jaw 14 is spaced-apart from cartridge assembly 16, and a closedposition, wherein the second jaw 14 is in close cooperative alignmentwith cartridge assembly 16, to clamp tissue therebetween. The second jaw14 may be pivotally mounted to the first jaw 12.

Referring to FIGS. 3-5, the jaw housing 18 includes a drive assemblyincluding an axial drive screw 20 for transmitting the rotational driveforces exerted by one or more drive shafts (not explicitly shown) of theadapter 200 (FIG. 1) to a drive screw nut 38 during a staplingprocedure. The drive screw 20 is rotatably supported in the jaw housing18 and includes a threaded portion 26 and a proximal engagement portion27. The threaded portion 26 of the drive screw 20 extends through a bore29 (FIG. 5) defined through a drive beam 28, such that the drive screw20 rotates freely within the bore 29 of the drive beam 28. The drivebeam 28 travels in a longitudinal direction along a longitudinal axis“A-A” defined by the drive screw 20, as will be described in detailbelow.

The drive beam 28 is slidably and non-rotatably disposed within the jawhousing 18 and includes a vertical support strut 34 and an abutmentsurface 36 that engages a drive screw nut 38. The drive beam 28 alsoincludes a cam member 40 disposed on top of the vertical support strut34. The vertical strut 34 is translatable through a longitudinal slot 44(FIG. 2) defined by an exterior camming surface 42 (FIG. 2) of thesecond jaw 14. In use, the cam member 40 engages the exterior cammingsurface 42 of the second jaw 14 and translate therealong toprogressively close the second jaw 14 relative to the first jaw 12 tocapture body tissue therebetween before ejecting the fasteners 310 (FIG.5).

Continuing with reference with FIGS. 3-5, a latch 46 is shown includingfirst and second elongated portions, links, or bars 48 a, 48 b, whichare pivotally coupled at their proximal ends to the drive beam 28 via afirst pin 50. The pin 50 extends through the vertical support strut 34adjacent a proximal end of the drive beam 28.

The first and second elongated portions 48 a, 48 b are connected to oneanother at their distal ends 52 a, 52 b via bridge 54 and a second pin58. The second pin 58 includes side protrusions 57 a, 57 b that extendlaterally from the distal ends 52 a, 52 b of the first and secondelongated portions 48 a, 48 b, and the bridge 54. The bridge 54 ismovable in and out of engagement with a recess 56 that is formed in anouter surface of the drive screw nut 38 and that is defined adjacent aproximal end thereof.

First and second cam members 60 a, 60 b are positioned within the jawhousing 18 and are coupled, e.g., screws, rivets or the like, to aninternal wall of the jaw housing 18. Each of the first and second cammembers 60 a, 60 b define a respective first and second cam slots 61 a,61 b therein. The first and second cam slots 61 a, 61 b each include arespective first cam portion 62 a, 62 b and a respective second camportion 64 a, 64 b. In embodiments, only one of the cam members 60 a, 60b is utilized and the other is omitted. Moreover, while the first andsecond cam slots 61 a, 61 b are described herein as being defined on thefirst and second cam members 60 a, 60 b, it is in the purview of theinstant disclosure that the first and second cam members 60 a, 60 b canbe omitted and the first and second cam slots 61 a, 61 b can simply bedefined within the internal wall of the jaw housing 18.

The drive screw nut 38 includes a threaded bore 39 (FIG. 5) that isthreadably coupled to the threaded portion 26 of the drive screw 20 suchthat as the drive screw 20 is rotated, the drive screw nut 38 translatesalong the longitudinal axis “A-A” defined by the drive screw 20. Thedrive screw nut 38 longitudinally translates the drive beam 28 when thedrive screw nut 38 is coupled to the drive beam 28 via the bridge 54, aswill be described in greater detail below. The drive screw nut 38 isconfigured to engage the sled 22 of the cartridge assembly 16 (FIG. 2)to eject the fasteners 310 from the cartridge 16 as detailed below.

The sled 22 includes outwardly and laterally extending flanges 24 anddefines a channel 25 (FIG. 9) therebetween. The sled 22 is positionedover the drive screw 20 receiving the drive screw 20 in the channel 25such that the channel 25 guides translation of the sled 22 along thelongitudinal axis A-A. The sled 22 has upstanding cam wedges 23configured to exert a fastener driving force on pushers 312 of thecartridge assembly 16, which drive the fasteners 310 from cartridgeassembly 16. Advancement of the drive screw nut 38 through cartridgeassembly 16 translates the actuation sled 22 such that the angledleading edges of cam wedges 23 sequentially contact the pushers 312causing the pushers 312 to translate vertically, thereby urging thefasteners 310 from cartridge assembly 16.

In use, initially, the drive beam 28 of the drive assembly is in a homeor retracted position with the bridge 54 of the latch 46 positionedwithin the recess 56 of the drive screw nut 38 as shown in FIGS. 3-6. Inthis position, a user can couple a fresh, new, unspent cartridgeassembly 16 to the jaw housing 18 of the first jaw 12.

When the surgical stapler is fired, the drive screw 20 is rotated, e.g.,in a clock-wise direction, and the drive screw nut 38 advances distally.As the drive screw nut 38 advances, the drive screw nut 38 pulls thedrive beam 28 distally to close the second jaw 14 by translating thevertical support strut 34 through the slot 44 such that the cam member40 cams against external camming surface 42 to approximate the first andsecond jaws 12, 14. Moreover, as the drive beam 28 is advanced, the sideprotrusions 57 a, 57 b of the second pin 58 slide through the first andsecond cam slots 61 a, 61 b of the first and second cam members 60 a, 60b. The bridge 54 of the latch 46 remains positioned within the recess 56of the drive screw nut 38 as the side protrusions 57 a, 57 b of thesecond pin 58 slide along the first cam portions 62 a, 62 b of the firstand second cam slots 61 a, 61 b. When the side protrusions 57 a, 57 b ofthe second pin 58 begin to slide along the second cam portions 64 a, 64b of the first and second cam slots 61 a, 61 b, the first and secondelongated portions 48 a, 48 b of the latch 46 begin to pivot about thedrive beam 28 via first pin 50 to gradually raise the bridge 54 fromwithin the recess 56 of the drive screw nut 38.

Referring to FIGS. 6-8, the drive beam 28 continues to advance distallytowards a first advanced position such that the bridge 54 is no longerpositioned within the recess 56 (e.g., the side protrusions 57 a, 57 bof the second pin 58 have slid to a distal end of the second camportions 64 a, 64 b). At this point, the lead screw nut 38 continues toadvance distally, without the drive beam 28. As the lead screw nut 38advances distally, the lead screw nut 38 engages the sled 22 to advanceor push the sled 22 distally towards a second advanced position. As thesled 22 advances, the sled 22 engages the pushers 312 via the cam wedges23 to eject the fasteners 310 from the cartridge assembly 16. It iswithin the scope of this disclosure that the lead screw nut 38 may pullthe drive beam 28 and simultaneously push the sled 22.

Once the cartridge assembly 16 is spent, or the stapling procedure isstopped, the drive screw 20 is rotated in an opposite direction, e.g.,in a counter clock-wise direction, which retracts the drive screw nut 38towards the retracted position. As the drive screw nut 38 retracts, thedrive screw nut 38 contacts the abutment surface 36 of the drive beam 28to push or retract the drive beam 28. As the drive beam 28 is retractedby the drive screw nut 38, the side protrusions 57 a, 57 b of the secondpin 58 slide proximally along the second cam portions 64 a, 64 b of thefirst and second cam slots 61 a, 61 b causing the first and secondelongated portions 48 a, 48 b of the latch 46 to pivot about the drivebeam 28 via first pin 50. The second cam portions 64 a, 64 b seat thebridge 54 back into the recess 56 of the drive screw nut 38. Inaddition, the weight of the bridge 54 and/or the second pin 50 mayassist in seating the bridge 54 back into the recess 56 of the drivescrew nut 38. It will be appreciated that when the drive screw nut 38 isretracted, the sled 22 remains in a distal position.

Once the drive screw nut 38 and drive beam 28 are in the retractedposition, a fresh cartridge assembly 16 can be coupled to the jawhousing 18 of the jaw 12 and the surgical stapler can then be firedagain.

From the foregoing and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications canalso be made to the present disclosure without departing from the scopeof the same. For example, the end effector 10 can be configured as anintegral unit in any of the embodiments disclosed herein. The endeffector 10 can be configured for use with a console and/or surgicalrobot, in any of the embodiments disclosed herein.

In embodiments, a resilient member (not shown) may be provided on thelatch 46 that is configured to urge the bridge 54 downwardly into recess56 of the drive screw nut 38.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Any combination ofthe above embodiments is also envisioned and is within the scope of theappended claims. Therefore, the above description should not beconstrued as limiting, but merely as exemplifications of particularembodiments. Those skilled in the art will envision other modificationswithin the scope and spirit of the claims appended hereto.

What is claimed is:
 1. An end effector comprising: first and second jawsmoveable relative to one another; a drive screw disposed within thefirst jaw and defining a longitudinal axis; a lead screw nut defining athreaded bore, the threaded bore receiving the drive screw, the leadscrew nut is advanced along the drive screw as the drive screw isrotated in a first direction and is retracted along the drive screw asthe drive screw is rotated in a second direction opposite the firstdirection; and a drive beam releasably coupled to the lead screw nutwhen the lead screw nut is in a retracted position, the drive beam beingpulled by the lead screw nut as the lead screw nut is advanced towards afirst advanced position, the drive beam decoupling from the lead screwnut as the lead screw nut is advanced to the first advanced positionsuch that the lead screw nut is advanced relative to the drive beam fromthe first advanced position to a second advanced position.
 2. The endeffector of claim 1, wherein the drive beam defines a passage thatreceives the drive screw therethrough.
 3. The end effector of claim 1further comprising a sled defining a channel, the channel receiving thedrive screw and configured to guide the sled along the drive screw. 4.The end effector of claim 3, wherein the lead screw nut is spaced apartfrom and positioned proximal to the sled in the retracted position. 5.The end effector of claim 3, wherein the lead screw nut engages aproximal surface of the sled at the first advanced position, the leadscrew nut pushing the sled distally as the lead screw nut is advancedfrom the first advanced position towards the second advanced position.6. The end effector of claim 5, wherein the first jaw includes acartridge assembly including staples disposed therein and as the leadscrew nut is advanced from the first advanced position towards thesecond advanced position the sled ejects the staples from within thecartridge assembly towards the second jaw.
 7. The end effector of claim6, wherein the cartridge assembly includes a staple pusher associatedwith each of the staples, the sled sequentially engaging the staplepushers to eject the staples from within the cartridge assembly.
 8. Theend effector of claim 5, wherein when the lead screw nut is retracted tothe first advanced position after pushing the sled the sled remainsstationary in a position between the first and second advancedpositions.
 9. The end effector of claim 8, wherein when the lead screwnut is retracted from the first advanced position towards the retractedposition, the lead screw nut pushes the drive beam towards the retractedposition and couples to the drive beam.
 10. The end effector of claim 1further comprising a latch including an elongated portion, the elongatedportion having proximal and distal ends, the proximal end of theelongated portion pivotally coupled to the drive beam, the distal end ofthe elongated portion including a bridge, the bridge received within anotch defined by the lead screw nut when the lead screw nut is in theretracted position to couple the drive beam to the lead screw nut. 11.The end effector of claim 10, wherein when the lead screw nut isadvanced towards the first advanced position the bridge is raised out ofthe notch to decouple the drive beam from the lead screw nut.
 12. Theend effector of claim 11, wherein when the lead screw nut is retractedfrom the first advanced position towards the retracted position, thebridge is lowered into the notch to couple the drive beam to the leadscrew nut.
 13. The end effector of claim 10 further comprising a cammember positioned adjacent the drive screw defining a cam slot, the camslot having a first portion parallel to the longitudinal axis of thedrive screw and a second portion extending distally from the firstportion at an angle relative to and away from the longitudinal axis ofthe drive screw, wherein the distal end of the elongated portionincludes a pin that is slidably received in the cam slot.
 14. The endeffector of claim 13, wherein the bridge is received in the notch whenthe pin is in the first portion of the cam slot and wherein the bridgeis raised out of the notch as the pin slides distally along the secondportion of the cam slot.
 15. A surgical instrument comprising: a handle;a shaft extending distally from the handle; and an end effectorsupported at a distal end of the shaft, the end effector comprising:first and second jaws moveable relative to one another; a drive screwdefining a longitudinal axis disposed within the first jaw; a lead screwnut defining a threaded bore, the threaded bore receiving the drivescrew, the lead screw nut is advanced along the drive screw as the drivescrew is rotated in a first direction and is retracted along the drivescrew as the drive screw is rotated in a second direction opposite thefirst direction; and a drive beam releasably coupled to the lead screwnut when the lead screw nut is in a retracted position, the drive beambeing pulled by the lead screw nut as the lead screw nut is advancedtowards a first advanced position, the drive beam decoupling from thelead screw nut as the lead screw nut is advanced to the first advancedposition such that the lead screw nut is advanced relative to the drivebeam from the first advanced position to a second advanced position. 16.A method of ejecting staples from a cartridge assembly, the methodcomprising: providing an end effector including: a first jaw; a drivescrew disposed within the first jaw and defining a longitudinal axis; alead screw nut defining a threaded bore, the threaded bore receiving thedrive screw; and a drive beam releasably coupled to the lead screw nutin a retracted position; coupling a cartridge assembly to the first jaw,the cartridge assembly including staples; advancing the lead screw nuttowards a first advanced position by rotating the drive screw in a firstdirection, the drive beam pulled by the lead screw nut, the drive beamdecoupling from the lead screw nut as the lead screw nut reaches thefirst advanced position; and advancing the lead screw nut from the firstadvanced position towards a second advanced position, the drive beamremaining stationary, the lead screw nut pushing the sled through thecartridge assembly to sequentially eject the staples.
 17. The method ofclaim 16, further comprising retracting the lead screw nut from thesecond advanced position towards the first advanced position by rotatingthe drive screw in a second direction opposite the first direction, thesled remaining stationary as the lead screw nut is retracted.
 18. Themethod of claim 17, further comprising retracting the lead screw nutfrom the first advanced position towards a retracted position and thedrive beam coupling to the lead screw nut as the lead screw nut isretracted from the first advanced position.
 19. The method of claim 16,wherein decoupling the drive beam includes raising a bridge of a latchoperatively associated with the drive beam out of a notch defined by thelead screw nut.
 20. The method of claim 18, wherein coupling the drivebeam to the lead screw nut includes lowering a bridge of a latchoperatively associated with the drive beam into a notch defined by thelead screw nut.
 21. A surgical end effector comprising: first and secondjaws moveable relative to one another; a driver element disposed withinthe first jaw and defining a longitudinal axis; and a drive memberreleasably coupled to the driver element, the drive member being pulledby the driver element towards a first advanced position and decouplingfrom the driver element upon reaching a predetermined positioncorresponding to a closed position of the first and second jaws, thesurgical end effector including a sled for firing staples from the firstjaw, the driver element moving the sled to fire staples after the drivemember is decoupled from the driver element.
 22. The surgical endeffector according to claim 21, wherein the drive member has the shapeof an I beam.
 23. The surgical end effector according to claim 22,wherein the driver element is a threaded member.
 24. The surgical endeffector according to claim 23, further comprising an internallythreaded nut.
 25. The surgical end effector according to claim 24,wherein the drive member is releasably coupled to the nut and the nut isthreadably engaged with the driver element.
 26. The surgical endeffector according to claim 25, wherein the drive member is releasablycoupled to the nut by a latch.
 27. The surgical end effector accordingto claim 26, further comprising a cam for disengaging the latch.
 28. Thesurgical end effector according to claim 24, wherein the nut is advancedalong the driver element as the driver element is rotated in a firstdirection and is retracted along the driver element as the driverelement is rotated in a second direction opposite the first direction.